Avoid syncing data twice for the 'publish_via_partition_root' option.

When there are multiple publications for a subscription and one of those
publishes via the parent table by using publish_via_partition_root and the
other one directly publishes the child table, we end up copying the same
data twice during initial synchronization. The reason for this was that we
get both the parent and child tables from the publisher and try to copy
the data for both of them.

This patch extends the function pg_get_publication_tables() to take a
publication list as its input parameter. This allows us to exclude a
partition table whose ancestor is published by the same publication list.

This problem does exist in back-branches but we decide to fix it there in
a separate commit if required. The fix for back-branches requires quite
complicated changes to fetch the required table information from the
publisher as we can't update the function pg_get_publication_tables() in
back-branches. We are not sure whether we want to deviate and complicate
the code in back-branches for this problem as there are no field reports
yet.

Author: Wang wei
Reviewed-by: Peter Smith, Jacob Champion, Kuroda Hayato, Vignesh C, Osumi Takamichi, Amit Kapila
Discussion: https://postgr.es/m/OS0PR01MB57167F45D481F78CDC5986F794B99@OS0PR01MB5716.jpnprd01.prod.outlook.com

1 files changed, 49 insertions, 10 deletions

diff --git a/src/backend/commands/subscriptioncmds.c b/src/backend/commands/subscriptioncmds.c
index 8a26ddab1c7..93a238412aa 100644
--- a/src/backend/commands/subscriptioncmds.c
+++ b/src/backend/commands/subscriptioncmds.c
@@ -1936,21 +1936,60 @@ fetch_table_list(WalReceiverConn *wrconn, List *publications)
 	WalRcvExecResult *res;
 	StringInfoData cmd;
 	TupleTableSlot *slot;
-	Oid			tableRow[3] = {TEXTOID, TEXTOID, NAMEARRAYOID};
+	Oid			tableRow[3] = {TEXTOID, TEXTOID, InvalidOid};
 	List	   *tablelist = NIL;
-	bool		check_columnlist = (walrcv_server_version(wrconn) >= 150000);
+	int			server_version = walrcv_server_version(wrconn);
+	bool		check_columnlist = (server_version >= 150000);
 
 	initStringInfo(&cmd);
-	appendStringInfoString(&cmd, "SELECT DISTINCT t.schemaname, t.tablename \n");
 
-	/* Get column lists for each relation if the publisher supports it */
-	if (check_columnlist)
-		appendStringInfoString(&cmd, ", t.attnames\n");
+	/* Get the list of tables from the publisher. */
+	if (server_version >= 160000)
+	{
+		StringInfoData pub_names;
 
-	appendStringInfoString(&cmd, "FROM pg_catalog.pg_publication_tables t\n"
-						   " WHERE t.pubname IN (");
-	get_publications_str(publications, &cmd, true);
-	appendStringInfoChar(&cmd, ')');
+		tableRow[2] = INT2VECTOROID;
+		initStringInfo(&pub_names);
+		get_publications_str(publications, &pub_names, true);
+
+		/*
+		 * From version 16, we allowed passing multiple publications to the
+		 * function pg_get_publication_tables. This helped to filter out the
+		 * partition table whose ancestor is also published in this
+		 * publication array.
+		 *
+		 * Join pg_get_publication_tables with pg_publication to exclude
+		 * non-existing publications.
+		 *
+		 * Note that attrs are always stored in sorted order so we don't need
+		 * to worry if different publications have specified them in a
+		 * different order. See publication_translate_columns.
+		 */
+		appendStringInfo(&cmd, "SELECT DISTINCT n.nspname, c.relname, gpt.attrs\n"
+						 "       FROM pg_class c\n"
+						 "         JOIN pg_namespace n ON n.oid = c.relnamespace\n"
+						 "         JOIN ( SELECT (pg_get_publication_tables(VARIADIC array_agg(pubname::text))).*\n"
+						 "                FROM pg_publication\n"
+						 "                WHERE pubname IN ( %s )) AS gpt\n"
+						 "             ON gpt.relid = c.oid\n",
+						 pub_names.data);
+
+		pfree(pub_names.data);
+	}
+	else
+	{
+		tableRow[2] = NAMEARRAYOID;
+		appendStringInfoString(&cmd, "SELECT DISTINCT t.schemaname, t.tablename \n");
+
+		/* Get column lists for each relation if the publisher supports it */
+		if (check_columnlist)
+			appendStringInfoString(&cmd, ", t.attnames\n");
+
+		appendStringInfoString(&cmd, "FROM pg_catalog.pg_publication_tables t\n"
+							   " WHERE t.pubname IN (");
+		get_publications_str(publications, &cmd, true);
+		appendStringInfoChar(&cmd, ')');
+	}
 
 	res = walrcv_exec(wrconn, cmd.data, check_columnlist ? 3 : 2, tableRow);
 	pfree(cmd.data);